Don't sweat it - sometimes we all have off nights, and sometimes newbies get the better of us when we think they shouldn't (remember this post of mine? http://www.fightingarts.com/ubbthreads/s...#Post16004740).
I usually can tap (or at least dominate positionally) most folks in class with less training time in than me. The key word here is "usually" - sometimes a new guy comes in who is so much bigger, stronger, and faster that my technique and kinesthetic (sp?) understanding of jiu-jitsu is not up to par to dealing with those attributes. This is frustrating, but I try my best to just relax and work my technique the best I know how. Eventually I will have an "ah-ha!" moment where it will all come together, and then my opponent's attributes won't mean squat. I know this, because it has happened before, and I am sure if I just keep training it will happen again
In the meantime, recall that you are WAY better on the mat now than when you started. I am sure the Matt of today could tap the Matt of 2.5 yrs ago in 30 seconds flat